It is said that imitation is the sincerest form of flattery. This is not a Twin Cam or Deluxe wheel. It is a decorative dummy center hub to hold the spinner with an otherwise stock 1600 type steel wheel (with the hubcap retaining pegs removed). They still bolt on, no splines. The dummy spinner hub is a cute accessory, but not very convincing. The 1600 type wheels (at right) look nothing like Twin Cam or "Deluxe" wheels (below).

In July 1988 at NAMGAR GT 12 in Marrietta, Ohio, I saw John Twist do a double take when he saw those things on a friend's MGA. It took him about three seconds to figure it out, which was longer than I thought it should take him, but maybe he hadn't seen them before. In the 50's and 60's you could find these advertised in the classifieds pages of many car magazines, sold by the likes of MG Mitten for instance.

Here's another one from RE Engineering, Inc, "NOKOF" Hub Caps, even less convincing, shown bolted over an MGA 1500 disc wheel.

Not quite sure how this is supposed to work, since the MG wheels are "lug-centric", meaning the wheels are centered by the lug nuts, not guided by the center hole. Maybe it didn't work.